/* Simple GPS Odometer v2

   David Johnson-Davies - www.technoblogy.com - 9th July 2018
   ATtiny2313 @ 8 MHz (external crystal; BOD disabled)
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

// Seven-segment definitions
const int charArrayLen = 12;
uint8_t charArray[] = {
//  ABCDEFG  Segments
  0b1111110, // 0
  0b0110000, // 1
  0b1101101, // 2
  0b1111001, // 3
  0b0110011, // 4
  0b1011011, // 5
  0b1011111, // 6
  0b1110000, // 7
  0b1111111, // 8
  0b1111011, // 9
  0b0000001, // 10  '-'
  0b0000000  // 11  Space
};

const int Dash = 10;
const int Space = 11;
uint8_t Buffer[] = { Dash, Dash, Dash, Dash};
uint8_t dp = -1;  // Decimal point position 0 to 3
uint8_t digit = 0;

uint8_t Digits[] = {14, 17, 15, 16};
// Segments must all go to port B; this specifies how they're wired up:
//                    g  f  e  d  c  b  a  dp
uint8_t Segments[] = {2, 4, 5, 3, 1, 6, 7, 0};

void ReorderBits() {
  uint8_t segs, newsegs;
  for (int i=0; i<charArrayLen; i++) {
    segs = charArray[i];
    newsegs = 0;
    for (int i=0; i<8; i++) {
      newsegs = newsegs | ((segs & 1)<<Segments[i]);
      segs = segs >> 1;
    }
    charArray[i]=newsegs;
  }  
}

void DisplayNextDigit() {
  pinMode(Digits[digit], INPUT);
  digit = (digit+1) % 4;
  uint8_t segs = charArray[Buffer[digit]];
  // Display decimal point?
  if (digit == dp) segs = segs | (1<<Segments[7]);
  DDRB = 0;     // All inputs
  PORTB = segs; // 1 = high
  DDRB = segs;  // 1 = output
  pinMode(Digits[digit], OUTPUT);
  digitalWrite(Digits[digit], LOW);
}

// Display a four/five digit decimal number
void Display (unsigned int number) {
  boolean dig = false;
  int j;
  if (number>9999) { j=10000; dp=2; }
  else { j=1000; dp=1; }
  for (int d=0; d<4 ; d++) {
    int i = (number/j) % 10;
    if (!i && !dig && j>100) Buffer[d]=Space;
    else { Buffer[d]=i; dig = true; }
    j=j/10;
  }
}

// ParseGPS
// Example: $GPRMC,194509.000,A,4042.6142,N,07400.4168,W,2.03,221.11,160412,,,A*77
const char fmt[] PROGMEM =
           "$GPRMC,dddtdd.ddm,A,????.????,?,?????.????,?,djdk,???.??,??????,,,?*??";

int state = 0;
unsigned int temp;

// GPS variables
volatile unsigned int Time, Msecs, Knots;
volatile boolean Fix;

void ParseGPS (char c) {
  if (c == '$') { state = 0; temp = 0; }
  uint8_t mode = pgm_read_byte_near(fmt + state++);
  // If received character matches format string, or format is '?' - return
  if ((mode == c) || (mode == '?')) return;
  // d=decimal digit
  uint8_t d = c - '0';
  if (mode == 'd') temp = temp*10 + d;
  // t=Time - hhmm
  else if (mode == 't') { Time = temp*10 + d; temp = 0; }
  // m=Millisecs
  else if (mode == 'm') { Msecs = temp*10 + d; temp = 0; }
  // j/k=Speed - in knots*100
  else if (mode == 'j') { if (c != '.') { temp = temp*10 + d; state--; } }
  else if (mode == 'k') { Knots = temp*10 + d; Fix = 1; }
  else state = 0;
}

// Timer interrupt - multiplexes display
ISR (TIMER1_COMPA_vect) {
  DisplayNextDigit();
}

// USART interrupt - receives data from GPS module
ISR (USART_RX_vect) {
  uint8_t c = UDR;
  ParseGPS(c);
}

void setup() {
  ReorderBits();
  // Set up Timer1 to multiplex the display
  TCCR1A = 0<<WGM10;
  TCCR1B = 1<<WGM12 | 2<<CS10;  // Divide by 8
  OCR1A = 4999;                 // Compare match at 200Hz
  TIMSK |= 1<<OCIE1A;           // Compare match interrupt enable
  // Set up USART
  UCSRB = 1<<RXEN | 1<<RXCIE;   // Enable Rx and interrupt
  UCSRC = 3<<UCSZ0;             // 8-bit UART mode
  UBRRL = 51;                   // 9600 baud
}

// Lowest GPS speed at which you are considered to be stationary
const int Stationary = 100;
long Distance;

void loop() {
  unsigned int temp;
  // Wait for fresh data
  while(!Fix);
  cli(); temp = Knots; sei();
  if (temp > Stationary) Distance = Distance + temp;
  Display(Distance*19/59438);
  Fix = 0;
}